The invention relates to a countermass for so-called recoilless weapons of the kind which include a barrel which is open at both ends and which, when fired, produce a rearwardly directed impulse or thrust which counteracts the recoil forces engendered by the fired projectile. The countermass is positioned behind the propulsive charge and exits together with the rearwardly exiting propellant gases as the projectile is propelled forwards.
In order to obtain a recoilless weapon, an additional propellant charge has been place behind the projectile and the gas generated thereby is caused to be blown-out rearwardly through an outflow nozzle. This results in a rearwardly directed momentum which can be adapted so as to be equal to the forwardly directed momentum of the projectile. Such a so-called "backblast weapon" produces behind the weapon a pressure of such high magnitude that its effect on the operating personnel places limits on the capacity of the weapon concerned, i.e. on the weight and the muzzle velocity of the projectile used.
It is known to position a countermass behind the propulsive charge, in order to increase the rearwardly directed momentum and therewith increase the capacity of the weapon, without generating excessively high pressure behind the weapon. The countermass is intended to move rapidly rearwards in the barrel, and is normally constructed so that it is vapourized or pulverized behind the weapon. The countermass is normally accelerated as a rigid body in the barrel and then pulverized subsequent to its exit from the barrel. One drawback with known countermass weapons, however, is that they are either too heavy or generate an excessive high risk zone behind the weapon. Compared with existing rocket-type "backblast weapons", the gains have been small both with regard to the effectiveness of the weapon and with regard to the negative effect that the pressure has on the operating personnel.
It is possible to extend the acceleration path of the projectile, so as to increase the muzzle velocity of a given projectile without increasing the size of the propellant charge at the same time. However, this requires a similar extension of the countermass acceleration, or requires the weight of said countermass to be considerably increased. Each increase in the length of the weapon or its weight has a limiting effect on the ease with which the weapon can be handled, and earlier attempts to improve the capacity of recoilless weapons have often resulted in excessively bulky weapons. Weapons whose capacity has been improved by increasing the maximum pressure in the barrel have also resulted in a heavier weapon, since this improvement requires heavy dimensioning of the barrel.